Providing reliable high data rate services, e.g. real-time multimedia services, over wireless and mobile communication channels is a paramount goal in developing coding and modulation schemes. When a data rate for wireless and mobile communication channels is high in relation to bandwidth, multipath propagation causes frequency-selective propagation while carrier frequency offsets and mobility induced Doppler shifts cause time-selectivity. Time- and frequency-selective propagation effects cause performance degradation and constitute the bottleneck for increasing data rates.
In order to mitigate time- and frequency-selective propagation effects, channel state information (CSI) is collected at the receiver. CSI is acquired at a receiver either by relying on training symbols that are known a priori by the receiver or by relying only on the received information-bearing symbols to acquire CSI blindly. Relative to channel estimation schemes relying on training symbols, blind channel estimation schemes typically require longer sequences of symbols and entail higher complexity. Adaptive or decision directed methods for channel estimation offer reduced complexity alternatives but are prone to error propagation and are limited to slowly varying channels. Consequently, training-based channel estimation schemes remain attractive despite being suboptimal and bandwidth consuming because training-based schemes decouple symbol detection from channel estimation, thereby reducing complexity and relaxing the required identifiability conditions.